This invention relates generally to electric motor drive assemblies, and more particularly, to clutchless PSC motor drive assemblies.
In many applications, known motor drive systems, such as, for example, a washing machine motor drive system, often include a dual speed 4 pole/6 pole electric motor, typically a split phase or capacitor start motor, coupled to a transmission for driving external components, such as, for example, a clothes basket and an agitator rotatably mounted within a washing machine cabinet. The split phase and capacitor start motors typically require slipping mechanisms, such as slipping belts or clutches, to mechanically unload the motor during starting, and further typically employ switches, such as centrifugal switches, to de-energize a start winding of the motor. However, both the slipping mechanism and start winding cutout switch increase manufacturing and assembly costs of the drive systems, as well as potentially reduce the reliability of the system due to failure and malfunction of the slipping mechanism and cutout switch. Furthermore, split phase and capacitor start motors are susceptible to relatively high torque pulsations, which can produce unpleasant noise that may lead to line rejects in manufacturing operations or field rejects by consumers when the drive system is installed in, for example, a household appliance.
Some attempt has been made to alleviate mechanical reliability issues in drive systems by using sophisticated electronic controls, such as computer-controlled triac switch systems, in conjunction with reversible motors. However, these systems tend to increase, rather than reduce, manufacturing costs. Moreover, complicated control systems introduce more reliability variables into the motor drive system that can ultimately reduce system reliability.
Accordingly, it would be desirable to proved a dual speed motor drive system with improved performance and reliability while reducing manufacturing and assembly costs by eliminating slipping mechanisms and cutout switches.
In an exemplary embodiment of the invention a motor drive system includes an electric motor including a rotor shaft, a first main winding and a second main winding. The first and second main windings are selectively energizable to operate the motor at first and second speeds, and at least one of the windings is a permanent split capacitor winding. A transmission is coupled to the rotor shaft, and the rotor shaft engages the transmission without employing a clutch mechanism. The motor may start in either the first and second speeds with sufficient starting torque and low inrush currents to avoid tripping of circuit breakers and opening of fuses, and without added expense and reliability issues of slipping clutch mechanisms. Moreover, the PSC motor eliminates a need for start winding cutout switches, and produces relatively low torque pulsation relative to conventionally used split phase and capacitor start motors, thereby further increasing drive system reliability and customer satisfaction.
In a further exemplary embodiment, the motor drive system is employed in a vertical axis washing machine, and includes a rotor shaft including an integral pulley. A belt is coupled to the pulley and engages a washing machine transmission. Because the motor generates sufficient starting torque in either speed of the motor, slipping clutches and slipping mechanisms are unnecessary. The motor includes a first start winding for rotating the motor shaft with the first main winding, a second start winding for rotating the motor shaft with the second main winding, and an extended main winding for tuning a strength of the motor between operation of the motor with only the first and second main windings. More specifically, in one embodiment, the first start winding is a 2 pole start winding, and the second start winding is a 4 pole start winding. Thus, the motor is operable in 2 pole mode, 4 pole mode, and using the extended means at modes between the two pole mode and 4 pole mode. Thus, greater motor speed distinctions and improved system performance are achieved.
A drive system of increased reliability and performance is therefore provided at reduced manufacturing cost by elimination of clutch mechanisms and cutout switches, and further with a lower cost motor than conventionally uses appliance motors.